In general, a strut-type suspension is mainly used for a front wheel of a four-wheeled motor vehicle, and has a construction in which a strut assembly incorporating a hydraulic shock absorber in an outer cylinder formed integrally with a main shaft is combined with a coil spring. Among such suspensions, (1) there is a type of structure in which the axis of the coil spring is actively offset with respect to the axis of the strut, so as to allow the sliding of a piston rod of the shock absorber incorporated in that strut to be effected smoothly, and (2) there is another type of structure in which the axis of the coil spring is arranged in alignment with the axis of the strut. In the suspension of either structure, a bearing is disposed between a mounting member for a motor vehicle body and an upper spring seat of the coil spring to allow the rotation to be effected smoothly when the strut assembly rotates together with the coil spring by the steering operation.
Further, this bearing is required to have a performance which supports the vehicle body load (thrust load) and concurrently smoothly allows for the radial load due to the above-described suspension structure, i.e., in the case of the former structure, the radial load produced by the restoring force of the coil spring in the axial direction of the strut even in a stationary state since the axis of the coil spring is offset with respect to the axis of the strut, and in the case of the latter structure, the radial load occurring due to misalignment attributable to the difficulty in fabrication that the axis of the strut and the axis of the coil spring must be arranged in alignment with each other.